i) Field of the Invention
This invention relates to a fibrous polyamide or wool substrate having durable resistance to staining by acid colorants and to a method of rendering a fibrous polyamide or wool substrate durably resistant to staining by acid colorants.
ii) Description of Prior Art
Fibrous polyamide substrates, such as nylon carpeting and similar wool substrates are susceptible to staining by both naturally occurring and commercial acid colorants found in many common foods and beverages. The demand for reduced staining from such acid colorants has by and large been met by treatment with compositions comprising sulfonated naphthol or sulfonated phenol-formaldehyde condensation products as disclosed for example in the following patents: U.S. Pat. No. 4,501,591 Ucci and Blyth; U.S. Pat. No. 4,592,940 Blyth and Ucci; U.S. Pat. No. 4,680,212 Blyth and Ucci; U.S. Pat No. 4,780,099 Greshler, Malone and Zinnato; U.S. Pat. No. 4,865,885 Herlant and Al; or by treatment with compositions comprising sulfonated novolak resins together with polymethacrylic acid as disclosed in U.S. Pat. No. 4,822,373 Olson, Chang and Muggli.
The use of polymers or copolymers of methacrylic acid of low weight average molecular weight and low number average molecular weight is described in U.S. Pat. No. 4,937,123 Chang, Olson and Muggli.
The initial stain resistance properties imparted to polyamide or wool substrates, such as carpeting, that have been treated using the above mentioned compositions degenerate, significantly with each wet cleaning the substrate receives. Improved stain resistance after wet cleaning can be achieved by increasing the amount of the sulfonated hydroxy aromatic formaldehyde condensation products, in the stain resist product or by increasing the amount of stain-resist product initially applied to the substrate, however, this generally leads to discoloration caused by yellowing of the substrate initially and further discoloration upon exposure to oxides of nitrogen and/or light.
Stain-resist products currently available in the market place are generally based on dihydroxydiphenyl sulfone and phenol sulfonic acid condensed with an aldehyde in acid or alkaline media, or dihydroxy diphenyl sulfone and naphthalene sulfonic acid condensed with aldehyde in acid or alkaline media.
It is generally known that increasing the ratio of the dihydroxydiphenyl sulfone to the phenol sulfonic acid or naphthalene sulfonic acid increases the stain resistance properties of the resin and subsequently causes a higher degree of yellowing or discoloration initially and further discoloration upon exposure to oxides of nitrogen and/or light.
Conversely it is also evident that when the ratio of phenol sulfonic acid or naphthalene sulfonic acid to dihydroxydiphenyl sulfone increases the result is lower stain-resist properties and less discoloration.
The addition of a methacrylic resin in the form of methacrylic polymers and/or copolymers to the previously mentioned condensation products (novolak resin) as disclosed in U.S. Pat. No. 4,223,473 (Olson, Chang and Muggli ) allows the use of a novolak resin in smaller quantities with larger quantities of the methacrylic resin. With this combination of novolak resin and methacrylic resin, a major improvement in the light fastness or less discoloration is achieved due to the dramatically reduced percentage of novolak resin in the product mentioned above, which is adjusted to obtain a desired low level of discoloration while maintaining an acceptable level of durability to wash. The high level of initial stain resistance is supplied primarily by the methacrylic resin and. after wet cleaning the stain resistance is supposedly maintained by the novolak resin, the methacrylic resin having largely been removed during the wet cleaning process.